It’s not often that I’ll go the “I told you so route”, but this time it seems appropriate towards Richard Tol. Though maybe also a thank you might be in order with how decisive scientists rebutted Tol’s nonsensus. But before I go into that, a bit of context is needed.

That scientists agree that we’re causing global warming is nothing new if you’re keeping yourself up to date on scientific findings. This is inconvenient for those denying that there is a problem or want to downplay its consequences. If you manage to confuse the public into thinking that there is no consensus, or sow doubt about this, you’ll prevent people from acting:

Naomi Oreskes – The Key Strategy Of The Merchants Of Doubt: Attacking The Consensus

Like Oreskes said, spreading doubt is the most effective strategy a science denier has. This type of attack is crucial to maintain the gap between what scientists agree on and what the public thinks scientists agree on. This tactic is how the tobacco industry successfully delayed action against the harmful effects of smoking for decades.

This brings me to Richard Tol, though he is a bit of an odd duck among those that try to discredit the scientific consensus on global warming. The detail is that despite his repeated attacks on the consensus, he actually agrees that there’s a consensus. Tol has said that “There is no doubt in my mind that the literature on climate change overwhelmingly supports the hypothesis that climate change is caused by humans. I have very little reason to doubt that the consensus is indeed correct” and that “The consensus is of course in the high nineties. No one ever said it was not.”

Tol’s latest attack started months ago when he shared strange and misleading graphs about the consensus on global warming. It was his attempt to demonstrate that Cook 2013 is an outlier with the consensus it found. The strangest part about this attempt was that Tol used research that also found a high consensus on global warming among experts.

Before I contacted the authors of the cited studies I had already warned Tol that Verheggen, Doran, and Anderegg would not agree with the conclusions he was drawing from their reseach and data. The responses I published from the authors of the cited studies didn’t impress Tol. Neither did the authors engaging Tol directly have any effect on him.

The consensus that humans are causing recent global warming is shared by 90%–100% of publishing climate scientists according to six independent studies by co-authors of this paper. Those results are consistent with the 97% consensus reported by Cook et al (Environ. Res. Lett. 8 024024) based on 11 944 abstracts of research papers, of which 4014 took a position on the cause of recent global warming. A survey of authors of those papers (N = 2412 papers) also supported a 97% consensus. Tol (2016 Environ. Res. Lett.11 048001) comes to a different conclusion using results from surveys of non-experts such as economic geologists and a self-selected group of those who reject the consensus. We demonstrate that this outcome is not unexpected because the level of consensus correlates with expertise in climate science. At one point, Tol also reduces the apparent consensus by assuming that abstracts that do not explicitly state the cause of global warming (‘no position’) represent non-endorsement, an approach that if applied elsewhere would reject consensus on well-established theories such as plate tectonics. We examine the available studies and conclude that the finding of 97% consensus in published climate research is robust and consistent with other surveys of climate scientists and peer-reviewed studies.

This sums up perfectly all the problems with what Tol did to create his graphs. It also, again, highlights that expertise matters for measuring the consensus on global warming, which is something I also pointed out to Tol before I published my article. You can see the effect of expertise on the consensus very clearly in the following graph:

Level of consensus on AGW versus expertise across different studies (Cook 2016).

I’ll highlight one of those data points in this graph to illustrate how bad it is. Take note of the light green dot in the lower left corner, that one indicates a consensus on global warming of 12%. But that’s not a group of climate scientists.

This percentage is calculated from data used for the paper Verheggen 2014 and is from a group of people tagged as “unconvinced.” Verheggen explained to me that “This group consists to a large extent of signatories of public statements disapproving of mainstream climate science, many of whom are not publishing scientists. For example, some Heartland Institute staffers were also included.”

This is the same Heartland Institute which describes itself as “the world’s most prominent think-tank promoting scepticism about man-made climate change” by using a partial quote from The Economist. As Verheggen said “It is actually surprising that the level of consensus in this group is larger than 0%.”

I doubt that Tol ever expected that the authors he cited would rebut him repeatedly and this strongly. Tol not backing down in the face of those initial responses means I also need to thank him. Without him, all these scientists who investigated the consensus probably wouldn’t have gathered to write such a strong response confirming the robustness of the scientific consensus on global warming.

There’s now one paper summarizing the research about the scientific consensus on human caused global warming. It explains how important expertise is, how consensus arises and develops, and why highlighting such a consensus is important for increasing awareness and acceptance of global warming. The exact opposite of what science deniers want to be demonstrated.

The research agrees: Humans are causing climate change (consensus on consensus)

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Collin Maessen is the founder and editor of Real Skeptic and a proponent of scientific skepticism. For his content he uses the most up to date and best research as possible. Where necessary consulting or collaborating with scientists.

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The goal of Real Skeptic is to take a critical look at scientific claims and investigate what the scientific literature and experts say about it. As skepticism doesn’t start with the viewpoints and claims of others, and being skeptical about those does not make you a skeptic. Being a skeptic starts with examining your own viewpoints, the positions you hold, and the claims you make.